WO2022186357A1

WO2022186357A1 - Method for determining finish annealing conditions for oriented electromagnetic steel sheet, and method for manufacturing oriented electromagnetic steel sheet using said determination method

Info

Publication number: WO2022186357A1
Application number: PCT/JP2022/009253
Authority: WO
Inventors: 誠渡邉; 敬寺島; 拓弥山田
Original assignee: Ｊｆｅスチール株式会社
Priority date: 2021-03-03
Filing date: 2022-03-03
Publication date: 2022-09-09
Also published as: JPWO2022186357A1; CN116917508A; KR20230136178A; JP7168134B1; EP4273278A1; BR112023017753A2

Abstract

The present invention proposes a method which is for determining finish annealing conditions for an oriented electromagnetic steel sheet, and by which a high-quality oriented electromagnetic steel sheet, which meets strict quality requirements that have been implemented in recent years, can be manufactured at high yield due to having favorable film characteristics even in a part, such as an upper/lower part or an inwardly/outwardly winding part of a coil during finish annealing or the like, in which the characteristics of a forsterite underlying film easily deteriorate.　When determining the finish annealing conditions, information on the concentration of an enriched component in the whole length and whole width of a steel sheet subjected to decarburization annealing is obtained, the optimum function of product characteristics in the relationship between the enriched component and finish annealing control conditions is obtained in advance, and then, in consideration of the distribution of the finish annealing control conditions in the coil, the finish annealing control conditions are determined so that the area, where the deviation of the ultimately obtained product characteristics from the aforementioned optimum function is in the range of ±δ, is maximum in terms of the whole length and the whole width.

Description

METHOD FOR DETERMINING FINISH ANNEALING CONDITIONS FOR GRAIN-EDUCED ELECTRICAL STEEL AND METHOD FOR MANUFACTURING GRAY-ORIENTED ELECTRICAL STEEL USING THE DETERMINATION METHOD

The present invention relates to a method for determining finish annealing conditions for a grain-oriented electrical steel sheet. The present invention relates to a method for determining finish annealing conditions for grain-oriented electrical steel sheets for obtaining grain-oriented electrical steel sheets at a high yield.
The present invention also relates to a method for manufacturing a grain-oriented electrical steel sheet using the method for determining finish annealing conditions.

Electrical steel sheets are soft magnetic materials that are widely used as materials for iron cores of transformers and motors. Among them, grain-oriented electrical steel sheets are highly concentrated in the {110} <001> orientation, which is called the Goss orientation. However, due to its excellent magnetic properties, it is mainly used for the iron cores of large transformers.

The grain-oriented electrical steel sheet is obtained by hot-rolling a steel material containing a large amount of Si and then further cold-rolling the cold-rolled sheet. It is generally manufactured by coating and performing final annealing. The high degree of integration in the Goss orientation is achieved by holding the steel at a high temperature of 800° C. or higher for a long time to cause secondary recrystallization in the finish annealing.

In the finish annealing, secondary recrystallization is caused, and then the steel is heated to a high temperature of about 1200°C to discharge impurities in the steel, and the internal oxide film generated in the decarburization annealing process and MgO are mainly formed. A forsterite-based undercoating is formed by reacting with the annealing separator.

This undercoating has the effect of reducing iron loss by applying tension to the steel sheet, and also functions as a binder for the insulating coating that is subsequently deposited, contributing to the improvement of the insulating properties and corrosion resistance of the steel sheet.

Here, the internal oxide film formed during decarburization annealing is affected by the residual oxides in the previous process and the texture of the steel sheet surface, oxidation is performed by a non-equilibrium reaction, and decarburization occurs at the same time as oxidation. It is affected by complex oxidation behavior due to factors such as In addition, since such decarburization annealing is also annealing at a high dew point, it is extremely difficult to maintain a uniform atmosphere in the furnace, and uneven oxidation occurs on the front and back surfaces of the steel sheet, the coil ends and the center, and the like. The problem was that it was easy.

On the other hand, for finish annealing, the steel sheet wound into a coil is placed in an up-end state in which the coil axis is vertical in the finish annealing furnace, and is held at high temperature for a long time, so temperature unevenness in the coil is reduced. occurs. Due to this temperature unevenness, there is a problem that coating properties vary in the longitudinal direction and the sheet width direction of the coil.

In particular, the outer edges of the upper and lower ends of the up-ended coil are overheated during the final annealing, causing problems such as peeling of the undercoat and the occurrence of point defects. Therefore, there is a problem that the product yield tends to decrease.

In order to solve these problems, various techniques have been proposed to improve the magnetic properties and film properties, especially by devising the conditions of the finish annealing. For example, Patent Literature 1 proposes a method of promoting refinement of a steel sheet by repeating increases and decreases in furnace pressure in a specific temperature range of finish annealing.

In addition, Patent Document 2 discloses a method for improving the coil shape by using MgO with a limited angle of repose and bulkiness as an annealing separator and optimizing the winding tension of the coil after applying the annealing separator. Proposed.

In Patent Document 3, deterioration of magnetic properties and film properties is suppressed by using a sealing material with a specific grain size at the lower end of the inner cover when performing finish annealing in a hearth rotating box furnace. A method to do so is proposed.

Patent Documents 4 and 5 propose a method of increasing the flow rate of the atmospheric gas in the final annealing of the Bi-added steel sheet to increase the tension applied to the undercoating.

JP-A-2000-239736 Japanese Patent Application Laid-Open No. 2001-303137 JP-A-08-209248 JP-A-09-003541 JP-A-09-111346

However, in the method described in Patent Document 1, if a negative pressure is generated locally in the annealing furnace when the pressure is lowered, the atmosphere gas will enter the furnace and the atmosphere gas will burn abnormally, and the coating properties will deteriorate. It was likely to deteriorate.

Further, in the method described in Patent Document 2, although the coil shape is improved to some extent, increasing the winding tension tightens the coil, which impairs the flow of atmospheric gas between the coil layers and deteriorates the magnetic properties and film properties. , there was a fear.

The method of limiting the particle size of the sealing material described in Patent Document 3 to a specific size and the method of increasing the gas flow rate described in Patent Documents 4 and 5 have limitations in improving magnetic properties and coating properties. The problem remains that a sufficient improvement effect cannot be obtained.

As described above, the application of the techniques described in these patent documents certainly has gradually improved the film properties and magnetic properties.
However, it is still not sufficient to meet the strict quality requirements of recent years. In particular, defects in the undercoat properties that occur at the top and bottom of the coil (both ends in the coil width direction) and the inner and outer coils (both ends in the longitudinal direction) of the coil during finish annealing should be checked prior to product shipment. Therefore, the production yield of the grain-oriented electrical steel sheet is lowered, resulting in an increase in the production cost of the grain-oriented electrical steel sheet.

The present invention has been made in view of the above-described problems of the conventional technology, and its purpose is to improve the properties of the undercoat such as forsterite at the upper and lower parts of the coil and the inner and outer winding parts during finish annealing. A method for determining finish annealing conditions for grain-oriented electrical steel sheets for producing high-quality grain-oriented electrical steel sheets with a high yield that meets the above-mentioned strict quality requirements in recent years by imparting good coating properties to parts, and It is to propose a manufacturing method using the determination method.

As a result of intensive research conducted by the present inventors to solve the above problems,
The concentration of each of O, Si, Al, Mn, and P in the decarburized annealed sheet, or the state (intensity ratio) of the enriched components of the internal oxide film containing Fe ₂ SiO ₄ , SiO ₂ , and FeO as oxide-generating components, and The cause of the yield decrease is that the finish annealing conditions vary depending on the position in the coil.
However, with current manufacturing equipment, it is difficult to reduce the variation within the coil with respect to the state of the enriched components of the internal oxide film and the conditions of the finish annealing.
On the other hand, if it is possible to obtain a good undercoat by adjusting the conditions of the final annealing according to the state of the concentrated components of the internal oxide film, it is possible to reduce the deterioration of the undercoat in the coil. ,
I got the knowledge.
Based on these findings, the present inventors conducted further studies, constructed a control model that optimizes the yield from variations in the condition of the concentrated components of the internal oxide film and the conditions of the finish annealing within the coil, and completed the present invention. rice field.

That is, the present invention is as follows.
1. After hot-rolling a steel material for a grain-oriented electrical steel sheet, it is cold-rolled once or cold-rolled twice or more with intermediate annealing, and then subjected to decarburization annealing that also serves as primary recrystallization annealing. , After applying an annealing separator and winding into a coil shape, finish annealing is performed to form a base film, and then flattening annealing is performed to make a product sheet.
In determining the conditions for the finish annealing,
1) When the steel sheet after decarburization annealing is divided into a plurality of sections in the longitudinal direction and the width direction, the enriched component index (M) in the internal oxide film in the steel sheet after decarburization annealing for each section to obtain information about
2) Prior to the determination of the finish annealing conditions, the concentration component of the control item of the finish annealing is determined based on the evaluation result of the influence of the control item of the finish annealing on the properties of the undercoat with respect to the concentration component. deriving an optimal function f(M) for the index (M);
3) obtaining information for the entire steel sheet regarding the distribution of the control items for each section with respect to a plurality of candidate values that are set values (H) of the control items for the finish annealing;
4) Determining whether the distribution of control items for each section is within the range of a predetermined allowable value (±δ) with respect to f(M), and determining the total number of sections within the range of the allowable value selecting a set value (H) of the control item that maximizes the area from the plurality of candidate values;
A method for determining finish annealing conditions for grain-oriented electrical steel sheets.

2. The concentration component index (M) is any one of O concentration, Si concentration, Al concentration, Mn concentration, P concentration, Fe ₂ SiO ₄ intensity ratio, SiO ₂ intensity ratio and FeO intensity ratio on the steel plate surface Alternatively, the method for determining finish annealing conditions for a grain-oriented electrical steel sheet according to 1 above, wherein there are two or more types.

3. 1 or 2 above, wherein the control item of the finish annealing is any one or more of the temperature increase rate between 950 and 1100 ° C. of the final finish annealing, the atmosphere switching temperature, the homogenization heat treatment time, and the homogenization heat treatment temperature. A method for determining finish annealing conditions for a grain-oriented electrical steel sheet according to 1.

4. 4. A method for producing a grain-oriented electrical steel sheet, wherein the method for determining finish annealing conditions according to any one of 1 to 3 above is used.

According to the present invention, it is possible to stably produce a grain-oriented electrical steel sheet with excellent properties of the underlying coating regardless of the position in the longitudinal and width directions of the coil. Therefore, the present invention greatly contributes to improvement of product quality, improvement of yield, and reduction of manufacturing cost.

It is the figure which mapped distribution of P intensity of coil full length full width. FIG. 3 is a diagram showing the relationship between the atmosphere switching temperature with respect to the P strength of the steel sheet and the coating properties. FIG. 10 is a diagram simulating temperature distribution at a representative point of 830° C. during finish annealing in a coil. The optimum atmosphere switching temperature calculated from the P intensity of the entire coil length and width, and the estimated temperature obtained from the calculation at each coil position at the atmosphere switching temperature of 700 ° C., 800 ° C., and 900 ° C. It is the figure which mapped the difference.

First, the experiments that led to the development of the present invention will be described.
<Experiment 1>
C: 0.06 mass%, Si: 3.3 mass%, Mn: 0.07 mass%, Al: 0.016 mass%, S: 0.003 mass%, the balance being Fe and unavoidable impurities. After being made into a steel material (slab) by a continuous casting method, the slab is heated to 1380 ° C., hot-rolled to a hot-rolled plate with a thickness of 2.2 mm, and heated at 1000 ° C. for 60 seconds. After rolling sheet annealing, the sheet was first cold rolled to an intermediate sheet thickness of 1.8 mm, subjected to intermediate annealing under conditions of 1100° C. for 80 seconds, and then secondary cold rolled to a final sheet thickness of 0.8 mm. A 23 mm cold-rolled sheet was obtained.

Next, the cold-rolled sheet was heated at a rate of 100°C/s between 500 and 700°C during the heating process using a horizontal (horizontal) continuous annealing furnace, and further heated to 860°C. After that, decarburization annealing, which also serves as primary recrystallization annealing, was performed by holding at this temperature for 140 seconds. In this decarburization annealing, atmosphere gas with a vol% ratio of H ₂ :N ₂ =60:40 was supplied from above and below the annealing furnace.

Regarding the steel sheet after decarburization annealing, the intensity of P, which is one of the enriched components in the internal oxide film, was measured online using a fluorescent X-ray device before being wound into a coil (this intensity is the intensity of X-rays). Therefore, in the present invention, the intensity and the concentration (the amount of enrichment) may be understood as synonymous) were analyzed. At this time, an energy dispersion type fluorescent X-ray device was used, and the conditions were voltage: 50 kv and current: 10 mA. This P intensity analysis was performed every 50 mm in the plate width direction and every 50 m in the longitudinal direction to create a distribution map of the X-ray P intensity. This map is shown in FIG. The total length of the coil is 5000m and the total width is 1000mm.

From the figure, it can be seen that the X-ray P intensity varies gently within the range of 1.4 to 2.6 kcps in both the longitudinal direction and the width direction of the steel plate. This is considered to be due to the influence of the atmosphere gas flow in the annealing furnace and the surface properties of the steel sheet in the previous process.

An annealing separator obtained by slurrying a powder mainly composed of MgO containing 5 mass% titanium oxide and 0.1 mass% sodium borate with water is applied to the cold-rolled steel sheet after decarburization annealing on the surface of the steel sheet. After coating and drying, it was coiled for final annealing.

Next, finish annealing was performed by changing the atmosphere switching temperature, which is one of the control items in the finish annealing, to form an undercoating on the surface of the steel sheet. The uniformity of the undercoating on the product sheet after final annealing was evaluated. The results are summarized in FIG. 2 in terms of the relationship between the intensity of P in the internal oxide film of the steel sheet after decarburization annealing and the atmosphere switching temperature. Here, the uniformity of the undercoating was evaluated as "uniform" when the thickness of the coating had a constant uniform appearance, and as "partially defective" when there was a portion thinner than the surroundings.

From the above experimental results, it was found that a good coating can be obtained if the atmosphere switching temperature, which is one of the control items in the final annealing, is kept within an appropriate range according to the P strength.

This means that the higher the concentration of P and the lower the atmosphere switching temperature, the easier it is for the undercoat to form. Therefore, when the concentration of P is large and the atmosphere switching temperature is low, the formation of the undercoat is excessively accelerated, resulting in localized areas where the undercoat becomes excessively large, which easily peels off and deteriorates the properties of the undercoat. . On the other hand, the inventors believe that if the amount of concentration of P is small and the atmosphere switching temperature is high, the formation of the undercoat is delayed and the undercoat becomes thin overall, and in this case also the undercoat deteriorates. .

From FIG. 2, in the relationship between the P strength of the internal oxide film and the atmosphere switching temperature, the regions where the uniformity of the undercoat is ensured are 1080-100×(P strength)−180° C. and 1080-100×(P strength). It can be seen that it is in the region between +180°C. That is, the optimum value of the atmosphere switching temperature for finish annealing (also simply referred to as the optimum value in the present invention) can be calculated from 1080 - 100 x (P strength) (also referred to as the optimum function f (M) in the present invention), and The difference (in the present invention, also referred to as the allowable value δ) between this and the actual atmosphere switching temperature (also referred to as the set value (H) in the present invention) given from the H ₂ switching temperature of the finish annealing of the representative point described later is It was found that if the temperature is within 180° C., a good undercoat is formed. Therefore, the uniformity of the undercoating can be ensured by adjusting the atmosphere (for example, H ₂ ) switching temperature of the finish annealing according to the P intensity of the internal oxide film.

Note that the representative point is a measurement point with a thermocouple attached to the hearth at a position in contact with the winding lower part of the coil.
In addition, the set value (H) referred to in the present invention may be the temperature that the steel plate actually reaches, such as the actual atmosphere switching temperature mentioned above as an example, that is, the output value. The value of the so-called input such as the set temperature) and the value of what is actually controlled such as the amount of fuel gas and the amount of electric power input are acceptable, and if they are unified in one simulation, any of the above values It can be suitably used in the present invention.

Next, in order to simulate the temperature history of finish annealing, a separately prepared coil after application of an annealing separator was used, and a plurality of thermocouples were attached to the coil to perform finish annealing. and the temperature inside the coil was simulated using the finite element method.

The final annealing at this time is performed by heating between room temperature and 950°C at a temperature increase rate of 25°C/h in an _N2 atmosphere, and heating between 950 to 1100°C at a temperature increase rate of ₂₀ °C/h in an H2 atmosphere. The next recrystallization was completed. After that, purification treatment was performed by heating between 1100 and 1200° C. in an atmosphere of H ₂ at a rate of temperature increase of 10° C./h and maintaining the temperature at 1200° C. for 10 hours. In addition, each temperature mentioned above and the temperature applied to the following annealing are described as the representative temperature for control (the temperature at the representative point), which is the temperature of the thermocouple attached to the lower hearth in contact with the coil.

FIG. 3 shows the result of simulating the temperature distribution of the entire steel sheet in the coil by the finite element method when the temperature at the representative point during the annealing is 830° C. in this heat pattern. This figure is also shown with a 50 mm pitch in the width direction and a 50 m pitch in the longitudinal direction. The total length of the coil is 5000m and the total width is 1000mm.
From the results of FIG. 3, it can be seen that the temperature is the lowest near the representative point slightly below the center of the plate width of the coil middle winding portion, and the difference between the maximum temperature and the minimum temperature is about 200°C.

Based on this result, this experiment was further advanced according to the following procedures.
That is, the appropriate temperature for switching the atmosphere from N ₂ to H ₂ was calculated from the P intensity at each coil position using the above formula of 1080-100×(P intensity). In addition, the simulated temperature at each coil position at each time point of the atmosphere switching temperature at 700, 800, and 900° C., which were set candidate values (h _{0 ,} h _{1 ,} h ₂ ), was calculated. Then, the difference Δ between the calculated appropriate temperature for switching from _N2 to H2 and the simulated temperature at _each coil position was displayed by mapping. The results are shown in FIG.

As can be seen from FIG. 4, when the atmosphere switching temperature was set to 700°C, a region in which the absolute value of Δ exceeded 180°C (the above δ) was widely observed in the entire steel sheet on the hearth side of the middle winding coil. On the other hand, when the temperature was set at 900° C., regions where the absolute value of Δ exceeded 180° C. (the above δ) were generated between the outermost and innermost windings. On the other hand, at an intermediate temperature of 800° C., 99.8% of the area of the entire steel sheet was within the range of 180° C. (the above δ) or less, except for a very small portion of the coil ends.

Therefore, it was concluded that it is best to perform the final annealing at an atmosphere switching temperature of 800° C. for the above coil. That is, according to the results of this experiment, the set value (H) of the atmosphere switching temperature can be set to 800.degree. The finish annealing conditions were the same as those described above except for the atmosphere switching temperature.
After that, the annealing separating agent was removed, a coating agent mainly composed of phosphate was applied, and flattening annealing was performed while baking. The coating appearance of this coil was determined by a surface inspection device, and uniform appearance without unevenness in color tone or dot-like defects in the coating was regarded as acceptable for the coating. As a result, a high coating pass rate of 99.7% was obtained. In this evaluation, since the insulating coating (here, the glass coating mainly composed of phosphate) is transparent, it can be considered that the acceptance rate of the coating reflects the properties of the underlying coating.

As described above, for each coil, the conditions in which the atmosphere switching temperature was changed as described above using the method of the present invention and the condition in which the atmosphere switching temperature was kept constant at 800° C. were performed for each 10 coils. Then, the film appearance was compared. As a result, the coating acceptance rate was as high as 99.7% when the atmosphere switching temperature was adjusted for each coil, whereas the coating acceptance rate was 91.7% when the switching temperature was kept constant at 800°C. It turned out to be 3%. It can be seen that by optimizing the switching temperature for each coil, the coating acceptance rate is significantly improved.
Here, the coating pass rate is the percentage of the surface area of the coil that has a uniform appearance. For example, if the surface area of the evaluated coil is 100,000 m ² and the surface area of the passed portion is 90,000 m ² , the pass rate is 90.0%.

That is, conventionally, the atmosphere switching temperature of the finish annealing was controlled using one representative point, so although the film characteristics at the representative point were good, there were defective parts over the entire coil length and width, resulting in a high yield. It was difficult to get good quality.
On the other hand, according to the present invention, the control that does not aim for a local optimum value and makes the range in which the coating properties are good the range that maximizes the area of the steel sheet wound into a coil (hereinafter simply referred to as the coil area). By performing the finish annealing under the set value (H) of the item (for example, the atmosphere switching temperature for the finish annealing), an effect of greatly improving the production yield was obtained.

In the present invention, as a procedure for maximizing the range in which the film characteristics are good as described above in terms of the coil area, a plurality of appropriate items among the various items conventionally used as control items are selected in advance, and a plurality of setting candidate values (h _0, _h _1, _h ₂ _{. . .} ), and the set value ( H) is most efficient.
In addition, in the laboratory, the undercoat was evaluated by variously changing the concentration component and the control item to be targeted, and the relationship between the amount of the concentration component and the control item that optimizes the properties of the undercoat was formulated. , determining an appropriate control item for each section from the amount of the thickening component, selecting the setting candidate value of the control item that has the maximum number of sections from the histogram for the number of sections among the setting candidate values of the control item, and selecting this selection There is a procedure for adopting the value as the set value (H) of the control item for finish annealing. As finish annealing, finish annealing including homogenization heat treatment or homogenization heat treatment and finish annealing may be performed separately, but both are simply referred to as finish annealing.
Alternatively, the same processing may be performed by obtaining a relational expression that provides a good coating from the value of the concentration component and the value of the control item in actual manufacturing.

These relationships are quantified in advance in the laboratory or by data analysis of production quality, and the set value (H), which is the condition of the control item for finish annealing, is determined in consideration of these relationships. . As control items, in addition to the atmosphere switching temperature described above, any one or more of the temperature increase rate between 950 and 1100 ° C. of the final finish annealing, the homogenization heat treatment time, and the homogenization heat treatment temperature can be used. . In the present invention, the control item means one or two or more items appropriately selected from the above four items.

A generalized description of the procedure of the present invention is as follows.
First, the concentration of the enriched component in the internal oxide film of the decarburization annealing is derived, for example, by monitoring or calculation for each section divided by a certain area in the width direction and the longitudinal direction of the steel sheet (this concentration Let the concentration of the component be M).
Next, the effect of the final annealing control items on the properties of the undercoating with respect to the above M is evaluated.
Based on these evaluation results, the relational expression f(M) between the above M and the control items that makes the properties of the undercoat good is obtained, and the allowable value ± δ that makes the properties of the undercoat good is obtained. .
Furthermore, in the same manner as the procedure described above, a plurality of setting candidate values (h _0, h _1, h ₂ . . . ) are selected and placed.
Also, regarding the control items related to finish annealing, the distribution of the actual (or calculated) control items on the steel sheet given by setting each of a plurality of setting candidate values (h _0, h _1, h _{2 . . .} ) is determined in advance by monitoring or calculation, for example, for each section divided by a certain area in the width direction and the longitudinal direction.

In addition, the finer the fixed area in the present invention, the finer the correspondence becomes possible. be. Therefore, it is practical and desirable to set the pitch in the width direction in the range of 1 to 400 mm and the pitch in the longitudinal direction in the range of 5 to 200 mm.

Using the above results, the set value (H) of the control item that maximizes the total area of the sections within the range of the allowable value ± δ is set to the set candidate value (h _0, h _1, h _2... ).
That is, the concentrated component in the internal oxide film, which is the monitoring index [concentrated component index (M)], is as described above. In addition, together with the monitoring of the concentration of the concentrated component in the coil after decarburization annealing, the optimum value of the control item for the finish annealing depending on the coil position is derived as described above.
Then, using the function f(M), the setting candidate values _h _0, h _1, h _{2 .} A setting value (H) is set from the setting candidate values (h _{0 ,} h _{1 ,} h ₂ .
As described above, such control items are any one or more of the heating rate between 950 and 1100 ° C. of the final finish annealing, the atmosphere switching temperature, the homogenization heat treatment time, and the homogenization treatment temperature. can be done. This is because the optimum ranges of these items tend to change depending on the quality of the decarburized annealed plate.

Note that the relationship f(M) between the control item and the monitoring index (concentration M) and δ can be obtained in advance in a laboratory or obtained by data analysis of the results of an actual machine.
The method of obtaining f (M) is not particularly limited, but specifically, when laboratory experimental results are used, a fluorescent X-ray spectrometer, FTIR, or the like is used to calculate the concentrated component of the decarburized annealing plate, and A regression equation can be obtained based on the results of observation of coating appearances of product sheets obtained by variously changing the finish annealing conditions to be adjusted. Alternatively, the above-mentioned product sheet may be subjected to an adhesion test conforming to JIS C2550, and a regression equation may be obtained based on the results of evaluating the film adhesion for each finish annealing condition. On the other hand, when data analysis is used, the comparison between the concentrated component strength of the decarburized annealed sheet and the conditions of the finish annealing is used, and the above acceptance criteria for the coating acceptance rate are used to obtain the regression equation with the coating adhesion acceptance rate. you should ask for

In addition, when using laboratory experimental results in the method of obtaining δ, the same equipment as in the method of obtaining f (M) is used, and if the test result is the appearance of the coating, for example, the pass/fail judgment is based on visual inspection. Alternatively, if it is an adhesion test of JIS C2550, based on the test pass value set for each user, the parameter is changed by about 20 to find the range in which the base film is good, and if the value in that range is halved, δ can be asked for. On the other hand, when data analysis is used, the same equipment and analysis tools as the method for obtaining f(M) above and the acceptance criteria for the above coating pass rate in the laboratory are used, and the parameters are also changed by about 20 to obtain a good undercoat. δ can be obtained by finding the range where It is also possible to set the optimum value and range using various machine learning algorithms such as SVM, random forest, principal component analysis, etc., without being limited to formulating using linear regression.

Next, other requirements in the present invention will be described.
The steel material (slab) used for the production of the grain-oriented electrical steel sheet subjected to the finish annealing whose conditions are determined using the present invention may be a conventionally known steel material used for the production of the grain-oriented electrical steel sheet. The specific composition of the steel material is as follows.
C: 0.01 to 0.10 mass%
If the C content is less than 0.01 mass%, the grain boundary strengthening effect of C is lost, and defects such as cracks in the slab occur that hinder production. On the other hand, if the C content exceeds 0.10 mass%, it becomes difficult to reduce the C content to 0.004 mass% or less at which magnetic aging does not occur in decarburization annealing. Therefore, C is preferably in the range of 0.01 to 0.10 mass%. More preferably, the lower limit is 0.02 mass% and the upper limit is 0.08 mass%.

Si: 2.5 to 4.5 mass%
Si is an element necessary to increase the resistivity of steel and reduce iron loss. Such an effect is not sufficient at less than 2.5 mass%, while at more than 4.5 mass%, workability is lowered, making it difficult to roll and manufacture. Therefore, Si is preferably in the range of 2.5 to 4.5 mass%. More preferably, the lower limit is 2.8 mass% and the upper limit is 3.7 mass%.

Mn: 0.01 to 0.50 mass%
Mn is an element necessary for improving the hot workability of steel. The above effect is not sufficient if the content is less than 0.01 mass%. On the other hand, if it exceeds 0.50 mass %, the magnetic flux density of the product sheet will decrease. Therefore, Mn is preferably in the range of 0.01 to 0.50 mass%. More preferably, the lower limit is 0.02 mass% and the upper limit is 0.20 mass%.

Components other than C, Si and Mn differ depending on whether or not an inhibitor is used to cause secondary recrystallization.
First, when using an inhibitor to cause secondary recrystallization, for example, when using an AlN-based inhibitor, Al and N are respectively Al: 0.01 to 0.04 mass%, N: 0.003 It is preferably contained in the range of to 0.015 mass%. Further, when using an MnS/MnSe inhibitor, in addition to the amount of Mn described above, one or two of S: 0.002 to 0.03 mass% and Se: 0.003 to 0.03 mass% preferably contains If the amount of each added is less than the above lower limit, a sufficient inhibitor effect cannot be obtained. On the other hand, if the above upper limit is exceeded, the inhibitor remains undissolved during heating of the slab, resulting in deterioration of magnetic properties. The AlN-based and MnS/MnSe-based inhibitors may be used in combination.

On the other hand, when the inhibitor is not used to cause secondary recrystallization, the content of Al, N, S and Se, which are the inhibitor-forming components described above, is reduced as much as possible, and Al: less than 0.01 mass%, It is preferable to use a steel material with N: less than 0.005 mass%, S: less than 0.005 mass%, and Se: less than 0.005 mass%.

In the steel material used in the present invention, the balance other than the above components is substantially Fe and unavoidable impurities. Further, for the purpose of improving magnetic properties, in addition to the above components, Ni: 0.010 to 1.50 mass%, Cr: 0.01 to 0.50 mass%, Cu: 0.01 to 0.50 mass%, P: 0.005-0.50 mass%, Sb: 0.005-0.50 mass%, Sn: 0.005-0.50 mass%, Bi: 0.005-0.50 mass%, Mo: 0.005- 0.100 mass%, B: 0.0002 to 0.0025 mass%, Te: 0.0005 to 0.0100 mass%, Nb: 0.0010 to 0.0100 mass%, V: 0.001 to 0.010 mass%, Ti : 0.001 to 0.010 mass% and Ta: 0.001 to 0.010 mass%.

Next, a method for manufacturing a grain-oriented electrical steel sheet including finish annealing for which conditions are determined using the present invention will be described.
The slab, which is the steel material to be used in the above manufacturing method, is obtained by melting the steel having the chemical composition suitable for the present invention described above by a conventional refining process, and then by a known ingot casting-slabbing rolling method or continuous casting method. It may be manufactured, or it may be directly cast into a thin slab with a thickness of 100 mm or less.

The slab is heated to a predetermined temperature in accordance with a conventional method. For example, when an inhibitor-forming component is contained, it is heated to a temperature of about 1400° C., specifically a temperature of 1300 to 1450° C. to remove the inhibitor-forming component. After being dissolved in steel, it is hot rolled into a hot rolled sheet.

On the other hand, when it does not contain an inhibitor-forming component, it is heated to a temperature of 1250°C or less and then hot-rolled to obtain a hot-rolled sheet. In addition, when the inhibitor-forming component is not contained, hot rolling may be performed immediately after casting without heating.

In the case of using thin cast slabs, hot rolling may be performed, hot rolling may be skipped and the next step of hot-rolled sheet annealing may be performed, or when hot-rolled sheet annealing is not performed, cold rolling may be performed. You may proceed to the step of rolling. The conditions for hot rolling are not particularly limited as long as they are carried out in accordance with a conventional method.

The hot-rolled sheet after hot rolling is subjected to hot-rolled sheet annealing as necessary. The soaking temperature for this hot-rolled sheet annealing is preferably in the range of 800 to 1150° C. in order to obtain good magnetic properties. If the soaking temperature is less than 800°C, the effect of hot-rolled sheet annealing is not sufficient, the band structure formed by hot rolling remains, and the primary recrystallization structure with regular grains cannot be obtained, and secondary recrystallization is not performed. Development may be inhibited. On the other hand, if the soaking temperature exceeds 1150° C., the grain size after annealing of the hot-rolled sheet becomes too coarse, and it becomes difficult to obtain a primary recrystallized structure with regular grain size.

The hot-rolled sheet after hot-rolling or after hot-rolled sheet annealing, and the thin cast slab are cold-rolled once or cold-rolled twice or more with intermediate annealing to form a cold-rolled sheet having a final thickness. do. The annealing temperature of the intermediate annealing is preferably in the range of 900-1200°C. If the annealing temperature is less than 900° C., the recrystallized grains after intermediate annealing become finer, and the number of Goss nuclei in the primary recrystallized structure may decrease, resulting in deterioration of the magnetic properties of the product sheet. On the other hand, if the annealing temperature exceeds 1200° C., the crystal grains become too coarse and it becomes difficult to obtain a primary recrystallized structure with regular grains, as in hot-rolled sheet annealing.

In addition, cold rolling (final cold rolling) to obtain the final plate thickness adopts warm rolling in which the steel plate temperature is raised to 100 to 300 ° C., or a temperature of 100 to 300 ° C. It is preferable to perform an inter-pass aging treatment in which the aging treatment is performed once or more than once. This improves the primary recrystallization texture and further improves the magnetic properties.

The cold-rolled sheet with the final thickness is subjected to decarburization annealing that also serves as primary recrystallization annealing. Here, in the heating process of the decarburization annealing, it is preferable to perform rapid heating at a temperature rising rate of 50° C./s or more between 500 and 700° C. up to the soaking temperature. As a result, the secondary recrystallized grains are refined and the core loss characteristics are improved. Further, the soaking temperature for decarburization annealing is preferably 780 to 950° C., and the soaking time is preferably 80 to 200 seconds. If the soaking temperature is lower than 780° C. or the soaking time is shorter than 80 seconds, insufficient decarburization or insufficient primary grain growth will occur. On the other hand, when the soaking temperature exceeds 950° C. or the soaking time exceeds 200 seconds, the grain growth of the primary recrystallized grains proceeds excessively. More preferably, the soaking temperature is 800-930° C. and the soaking time is 90-150 seconds.

The atmosphere during soaking in the decarburization annealing is preferably a wet hydrogen atmosphere in which the dew point is adjusted and the oxygen potential PH ₂ O/PH ₂ is in the range of 0.3 to 0.6. When the PH ₂ O/PH ₂ ratio is less than 0.3, decarburization is insufficient, while when it exceeds 0.6, FeO tends to form on the surface of the steel sheet, degrading the coating properties. More preferably, it is in the range of 0.4 to 0.55. The oxygen potential PH ₂ O/PH ₂ of the atmosphere during heating for decarburization annealing does not need to be the same as during soaking, and may be controlled separately.

Furthermore, the atmosphere during soaking does not need to be constant. For example, the soaking process may be divided into two stages, and the oxygen potential PH ₂ O/PH ₂ in the latter stage may be a reducing atmosphere of 0.2 or less. As a result, the morphology of the internal oxide film formed on the surface layer of the steel sheet is improved, which is advantageous in improving the magnetic properties and film properties. A more preferable PH ₂ O/PH ₂ in the latter stage is 0.15 or less. Also, the time ratio between the former stage and the latter stage is not particularly limited, but the latter stage is preferably about 25% or less of the former stage.

Here, what is important in the present invention is to monitor a specific index [concentrated component index (M)] for the internal oxide film of the decarburized annealed sheet in the width direction and the longitudinal direction. As a specific index [concentrated component index (M)] for the internal oxide film, for example, the detection intensity of the elements such as O, Si, Al, Mn, and P on the surface of the steel plate by X-rays, gamma rays, infrared spectroscopy, etc. That is, the degree of enrichment (M) of the element, or the detection intensity ratio of the surface layer of the product of FeO, Fe ₂ SiO ₄ , and SiO ₂ , that is, the degree of enrichment (M) of the product can be used.

Various analyzes such as X-rays, gamma rays, and infrared spectroscopy can be used to detect the above elements. Also, the analysis conditions are not particularly limited, although voltage of 10 to 60 kV and current of 1 to 30 mA are generally used, for example, when fluorescent X-ray analysis is used. In general, if the voltage is increased, information on the inside of the steel sheet can be obtained. It is also possible to use a combination of these measured values for the detection of the above elements. Alternatively, if there is already sufficient data, or if a change in strength at a specific position can be predicted from the characteristics of the apparatus, the concentration distribution may be derived by numerical simulation from the decarburization annealing temperature and atmospheric conditions.

The above online analysis is desirably performed after decarburization annealing until the annealing separator is applied, but if the annealing separator does not contain the element to be measured, it may be performed after the application. .
In the above online analysis, it is desirable to perform the above-mentioned on-line analysis over both the front and back sides of the steel sheet over the entire length and width of the coil. If it is known, analysis of the site excluding it (for example, only the front side) is also acceptable.

For the cold-rolled sheet that has undergone decarburization annealing, an annealing separator containing MgO as a main component is slurried, applied to the surface of the steel sheet, and then dried. Here, the annealing separator contains 50 mass % or more of MgO as a main component. If the MgO content is less than 50% by mass, the main component for film formation is insufficient, and a good film cannot be obtained. Furthermore, the content of MgO is preferably 70 mass% or more.

In addition, conventionally known additives such as compounds such as Ti, Na, Al, Sb, and Ca can be appropriately added to the annealing separator mainly composed of MgO. In this case, the total content of the above compounds is less than 50 mass%. If the content of such a compound is 50 mass % or more, the content of MgO becomes less than 50 mass %, causing poor formation of the forsterite film. More preferably, the total content of such compounds is 30 mass% or less. Also, the amount of the annealing separator to be applied to the surface of the steel sheet, hydration temperature and time may be within known ranges and are not particularly limited.

The steel plate coated with the annealing separator is then heated and held in an annealing furnace with the steel plate coil placed on the up end (standing in the coil axial direction) to cause secondary recrystallization and then purification. Apply final annealing to process. Such finish annealing is preferably carried out by heating to a temperature of 1100° C. or higher to cause secondary recrystallization. Here, in order to complete secondary recrystallization, when performing secondary recrystallization during temperature rise, the temperature range from 700 to 1100° C. should be raised at a rate of temperature increase of 2 to 50° C./h. is preferred. In addition, when secondary recrystallization is performed during the retention treatment, it is preferable to retain the temperature within the retention temperature range for 25 hours or more. In any case, the atmosphere at 500° C. or lower is an inert atmosphere such as N ₂ or Ar. Also, at any temperature between 500° C. and 1100° C., the inert atmosphere is switched to an atmosphere containing 5% or more of H ₂ . If the switching temperature is less than 500°C, there is a danger of explosion, while if it exceeds 1100°C, the period during which the inert gas is introduced becomes too long and the film deteriorates.

In the finish annealing, after secondary recrystallization, a forsterite coating (undercoating) is formed, and impurities contained in the steel sheet are discharged. Purification is performed at a temperature of 1120 to 1250 ° C. for 2 to 50 hours. Treatment is preferred. If the purification treatment temperature is less than 1120° C. or the holding time is less than 2 hours, the purification will be insufficient. On the other hand, if the temperature of the purification treatment exceeds 1250° C. or the holding time exceeds 50 hours, the coil will be buckled and deformed, resulting in a defective shape and a reduced yield. More preferably, the lower limit of the temperature of the purification treatment is 1150°C. On the other hand, the upper limit of the temperature of the purification treatment is 1230°C. More preferably, the lower limit of the holding time of the purification treatment is 3 hours. On the other hand, the upper limit of the holding time of the purification treatment is 40 hours.

In the present invention, before the finish annealing, a preliminary heat treatment may be performed by holding the steel sheet at a predetermined temperature for a predetermined time, and a homogenization heat treatment may be performed to homogenize the element concentrations on the front and back surfaces of the steel sheet. This homogenization heat treatment is preferably carried out under the conditions of holding at a temperature of 800 to 950° C. for 5 to 200 hours. If the temperature is less than 800° C. or the time is less than 5 hours, the above effect cannot be sufficiently obtained. On the other hand, if the temperature exceeds 950° C. or the time exceeds 200 hours, the activity of MgO is lost and the film properties deteriorate.

The homogenization heat treatment may be performed separately from the finish annealing, or may be incorporated in the first half of the finish annealing, and the homogenization heat treatment may be followed by the finish annealing. In addition, the conditions for the homogenization heat treatment overlap with the temperature range in which secondary recrystallization occurs. The step of causing recrystallization can be omitted.
In the present invention, the finish annealing conditions (control items) in such finish annealing may be at least one condition selected from the above-described finish annealing conditions, such as the conditions for homogenization heat treatment, and a plurality of conditions. You can choose any condition. Further, in the present invention, even if the homogenization heat treatment is performed separately from the finish annealing, the conditions of the homogenization heat treatment are regarded as one of the conditions of the finish annealing.

When the above homogenization heat treatment and finish annealing are performed separately, it is preferable that the heating rate from room temperature to the purification treatment temperature is in the range of 5 to 50° C./h on average. In addition, it is more preferable that the rate of temperature rise is an average of 8° C./h or more. On the other hand, it is more preferable that the rate of temperature increase be 30° C./h or less on average. Further, when the homogenization heat treatment is incorporated into the finish annealing, in the subsequent finish annealing after the homogenization heat treatment, the average temperature increase rate from the homogenization heat treatment temperature to the purification treatment temperature is in the range of 5 to 50 ° C./h. preferably. The average rate of temperature rise is more preferably 8° C./h or more. On the other hand, the average heating rate is more preferably 30° C./h or less.

Since the finish annealing is carried out in a coiled state, it takes a long time for heat diffusion, and a temperature difference occurs in the coil. Such a temperature difference may be 500° C. or more in some cases.
Therefore, even if the conditions for finish annealing are set based on the temperature history as described above, the temperature difference at each position (section) in the coil varies greatly depending on the position in the coil. must be understood by actual measurement or simulation.
As for the simulation method, any of various proposed temperature simulation methods such as the finite difference method and the finite element method may be used. Also, in calculating such a simulation, it is desirable to attach thermocouples and other temperature measuring devices to each part of the coil to measure the temperature and take it into account in the calculation, as this will further increase the calculation accuracy.

Using such a method, the monitoring result of the decarburized annealed sheet [concentrated component index (M)] and the control items of the finish annealing are matched as described above. As control items for the matching finish annealing, any one or more of the heating rate, the temperature for switching to the atmosphere containing H ₂ , the homogenization heat treatment time, and the homogenization heat treatment temperature can be appropriately selected.

Here, it is generally known that the optimum conditions for finish annealing change according to the quality of the internal oxide film formed by decarburization annealing. For example, in a decarburized annealed sheet in which a large amount of Fe oxide is formed in the internal oxide film, the Fe oxide decomposes during the final annealing to generate oxygen, which adversely affects the film. Therefore, it is effective to lower the introduction temperature of H ₂ in the annealing atmosphere to reduce the Fe oxide before the Fe oxide decomposes. On the other hand, under conditions where almost no Fe oxide is generated, the amount of the internal oxide film is small and the amount of the forsterite raw material is small. Therefore, it is necessary to replenish the oxygen component to the coating raw material by oxidation during the final annealing by increasing the introduction temperature of H ₂ during the final annealing.

Corresponding such a relationship with the indices described so far, the concentration (strength ) or the concentration (strength ratio) of either FeO or Fe ₂ SiO ₄ of the produced oxide increases, film formation is likely to occur, so the temperature increase rate during finish annealing, which is a control item for finish annealing, is reduced. It is effective to change conditions such as lowering the H ₂ -containing atmosphere switching temperature or shortening the homogenization heat treatment time.

_In addition, if the amount of Si in the decarburized annealed sheet increases, it becomes relatively difficult for the film to form. Prolonging the time is effective.

After the finish annealing, the steel sheet is preferably washed with water, brushed, pickled, or the like in order to remove the unreacted annealing separating agent adhering to the surface of the steel sheet, and then flattened and annealed for shape correction. This is because the finish annealing is performed in a state in which the steel sheet is wound around a coil, so that deterioration of the magnetic properties due to curling of the coil can be prevented.
In the case of laminating grain-oriented electrical steel sheets for use, it is preferable to have an insulating coating on the surface of the steel sheet. It is preferred to apply a imparting tensioning coating. The insulating coating may be applied during the planarization annealing, or may be performed before or after the planarization annealing.

In addition, magnetic domain refining treatment can be applied to further reduce iron loss. As a method for refining the magnetic domains, there are conventionally known methods, for example, forming grooves by etching the surface of a steel sheet that has been cold-rolled to the final thickness, or irradiating the surface of a product sheet with laser or plasma. A method of introducing linear or point-like thermal strain or impact strain can be used.

C: 0.05 mass%, Si: 3.6 mass%, Mn: 0.08 mass%, Al: 0.022 mass%, Se: 0.02 mass%, Sb: 0.07 mass%, the balance being Fe and unavoidable A steel material (slab) is produced by melting a steel containing toxic impurities and using a continuous casting method to form a steel material (slab). After performing hot-rolled sheet annealing for 60 seconds, primary cold rolling was performed to obtain an intermediate sheet thickness of 1.8 mm. A cold-rolled sheet having a final thickness of 0.23 mm was obtained.

Next, the cold-rolled sheet is passed through a horizontal (horizontal) continuous annealing furnace, heated between 500 and 700° C. at a heating rate of 500° C./s, and held at 800° C. for 150 seconds. Decarburization annealing was performed, which also served as primary recrystallization annealing. In this decarburization annealing, atmosphere gas with a vol% ratio of H ₂ :N ₂ =50:50 was supplied from above and below the annealing furnace. After the decarburization annealing was completed, the intensity ratio of Fe ₂ SiO ₄ , SiO ₂ and FeO was measured online using an infrared spectrometer before being coiled. The measured value is digitized as (Fe ₂ SiO ₄ intensity ratio) / (sum of each intensity ratio of SiO ₂ , Fe ₂ SiO ₄ , FeO), and this is divided into sections every 50 mm in the width direction and every 50 m in the longitudinal direction. I measured and made a map.

Furthermore, an annealing separator obtained by slurrying a powder mainly composed of MgO containing 6 mass% titanium oxide and 3 mass% strontium sulfate with water is applied to the surface of the steel sheet, dried, and formed into a coil for final annealing. After winding up, finish annealing was performed. Finish annealing was carried out by heating between room temperature and 900° C. in an N ₂ atmosphere at a heating rate of 10° C./h, and performing homogenization heat treatment at 900° C. for 12 to 60 hours. Subsequently, after heating between 900 to 950° C. and 950 to 1100° C. in an H ₂ atmosphere at a heating rate of 10° C./h to complete the secondary recrystallization, the temperature is heated between 1100 to 1200° C. in an H ₂ atmosphere. was heated at a rate of temperature increase of 10° C./h and held at a temperature of 1200° C. for 10 hours for purification.

Here, in setting the time for the homogenization heat treatment (homogenization heat treatment time), from the data analysis of the Fe ₂ SiO ₄ intensity ratio and the homogenization heat treatment time in the coil that had been performed until then, homogenization It has been confirmed that a good coating can be obtained if the heat treatment time is within ±20 hours as the difference ±δ from the time (optimal value) obtained from the following formula (1). The following equation (1) is the function f(M).
100−150×(Fe ₂ SiO ₄ intensity ratio) [h] (1)
Based on this, setting candidate values (h _0, h _1, h _{2 .} Then, the condition that the total area of the section where the difference ±δ from the (optimal value) obtained from the above formula (1) from the setting candidate values h _0, h _1, h _{2 …} is within ± 20 hours is maximum As the set value H, the homogenization heat treatment temperature is set to 900 ° C., and the homogenization heat treatment time is set to the above set value H for each coil based on the thermocouple installed on the hearth that is in contact with the inner winding portion of the coil. did.

After that, after removing the annealing separation agent remaining on the steel sheet, a coating agent is applied, and flattening annealing is performed in addition to baking to form an insulating film (a glass film mainly composed of phosphate) on the steel plate surface. did.
When manufacturing the above coils 10 times, each coil was subjected to homogenization heat treatment by setting the set value H according to the above procedure. The coating appearance of the 10 coils thus obtained was visually determined by a surface inspection device. The pass/fail judgment was made according to the criteria of Experiment 1 above.

As a result of such judgment, a high value of 99.8% was obtained for the above-mentioned coating pass rate on the average of 10 coils. On the other hand, without following the present invention, the homogenization heat treatment is uniformly performed at 900 ° C. for 10 coils, and the average value of the Fe ₂ SiO ₄ strength ratio of the entire steel plate is substituted into the above formula (1). : When the test was performed for 50 hours, the coating pass rate was 96.3% on the average of 10 coils.

C: 0.04 mass%, Si: 3.2 mass%, Mn: 0.08 mass%, Al: 0.006 mass%, Sn: 0.04 mass%, with the balance being Fe and unavoidable impurities. After being made into a steel material (slab) by a continuous casting method, the slab is heated to 1260 ° C., hot-rolled to a hot-rolled plate having a thickness of 2.8 mm, and hot-rolled at 1100 ° C. for 60 seconds. After performing sheet annealing, cold rolling was performed to obtain a cold-rolled sheet having a final sheet thickness of 0.23 mm.

Next, the sheet is passed through a horizontal (horizontal) continuous annealing furnace, heated at a rate of 300°C/s between 500°C and 700°C during the heating process, held at 820°C for 120 seconds, and continued at 850°C. Decarburization annealing, which also serves as primary recrystallization annealing, was performed for 30 seconds. In this decarburization annealing, atmosphere gas with a vol% ratio of H ₂ :N ₂ =50:50 was supplied from above and below the annealing furnace. After the decarburization annealing was completed, the intensity (concentration) distribution of each of O, Si, Al, Mn and P was measured on-line using a fluorescent X-ray device before being wound into a coil. The measured values were measured at intervals of 50 mm in the width direction and 50 m in the longitudinal direction to create a map.

Furthermore, an annealing separator obtained by slurrying a powder mainly composed of MgO containing 4 mass% titanium oxide and 2 mass% ammonium sulfate with water is applied to the surface of the steel sheet, dried, and formed into a coil for final annealing. After winding, finish annealing was performed. The final annealing is performed by heating between room temperature and 950°C at a heating rate of 10°C/h in an _N2 atmosphere, heating between 950°C and 1100° _C at various heating rates in an H2 atmosphere, and heating at 1100 to 1100°C. Purification treatment was performed by heating between 1200° C. in an H ₂ atmosphere at a temperature increase rate of 10° C./h and maintaining the temperature at 1200° C. for 10 hours.

Here, the procedure for setting the heating rate between 950 and 1100 ° C. is based on the data analysis of the strength of each element [concentrated component index (M)] and the heating rate in the coil that has been performed so far. , the optimum heating rate (optimal value) is obtained for each coil, and further, the heating rate (setting candidate values h _0, h _1, h _{2 …} ). Then, the difference between the optimum heating rate (optimal value) obtained from the intensity of each element and the heating rate at each position (each section of the coil) subjected to the temperature simulation is within a predetermined heating rate (δ). The setting candidate value that maximizes the area is set to the setting value H.
Specifically, f(O , Si, Al, Mn, P) = 8.8 x P (O) - 1.1 x P (Si) - 11 x P (Al) - 13 x P (Mn) + 6.0 x P (P) + 88 (°C/h ) (2)
The conditions were set so that the total area of the compartments where the difference ±δ from the (optimum value) obtained by (the optimum value) was ±4° C./h was maximized. Moreover, the temperature rise rate was set based on the measurement with a thermocouple installed on the hearth that was in contact with the inner winding portion of the coil. The above equation (2) is the function f(M).
After that, after removing the annealing separation agent remaining on the steel sheet, a coating agent is applied, and flattening annealing is performed in addition to baking to form an insulating film (a glass film mainly composed of phosphate) on the steel plate surface. did.
When the above coils were manufactured 10 times, the set value H was set according to the above procedure for each coil, and the temperature was raised between 950 and 1100°C. The coating appearance of the 10 coils thus obtained was visually determined by a surface inspection device. The pass/fail judgment was made according to the criteria of Experiment 1 above.

According to the present invention, the result of determination when the heating rate (H) that maximizes the (total) area of the range (section) where |f(M)−h ₀ |≦δ is set for each coil , an extremely high coating pass rate of 99.94% was obtained on the average of 10 coils. On the other hand, without following the present invention, 10 coils were uniformly heated at a rate of 10° C./h (a value obtained by substituting the average value of each strength into the above equation (2)). In this case, the coating pass rate was 96.5% on average for 10 coils.

Claims

After hot-rolling a steel material for a grain-oriented electrical steel sheet, it is cold-rolled once or cold-rolled twice or more with intermediate annealing, and then subjected to decarburization annealing that also serves as primary recrystallization annealing. , After applying an annealing separator and winding into a coil shape, finish annealing is performed to form a base film, and then flattening annealing is performed to make a product sheet.
In determining the conditions for the finish annealing,
1) When the steel sheet after decarburization annealing is divided into a plurality of sections in the longitudinal direction and the width direction, the enriched component index (M) in the internal oxide film in the steel sheet after decarburization annealing for each section to obtain information about
2) Prior to the determination of the finish annealing conditions, the concentration component of the control item of the finish annealing is determined based on the evaluation result of the influence of the control item of the finish annealing on the properties of the undercoat with respect to the concentration component. deriving an optimal function f(M) for the index (M);
3) obtaining information for the entire steel sheet regarding the distribution of the control items for each section with respect to a plurality of candidate values that are set values (H) of the control items for the finish annealing;
4) Determining whether the distribution of control items for each section is within the range of a predetermined allowable value (±δ) with respect to f(M), and determining the total number of sections within the range of the allowable value selecting a set value (H) of the control item that maximizes the area from the plurality of candidate values;
A method for determining finish annealing conditions for grain-oriented electrical steel sheets.
The concentration component index (M) is any one of O concentration, Si concentration, Al concentration, Mn concentration, P concentration, Fe 2 SiO 4 intensity ratio, SiO 2 intensity ratio and FeO intensity ratio on the steel plate surface The method for determining finish annealing conditions for a grain-oriented electrical steel sheet according to claim 1, wherein two or more types are used.
1 or 2, wherein the control items of the finish annealing are any one or more of a temperature increase rate between 950 and 1100° C. of the final finish annealing, an atmosphere switching temperature, a homogenization heat treatment time and a homogenization heat treatment temperature. 3. The method for determining finish annealing conditions for grain-oriented electrical steel sheets according to 2 above.
A method for producing a grain-oriented electrical steel sheet, characterized by using the method for determining finish annealing conditions according to any one of claims 1 to 3.